middleware/root: add it (#330)

This PR adds the *root* middleware that specifies a path where
all zone file (the *file* middleware is the only consumer now) can
be found. It works the same as in Caddy.

Documentation can be found in the README.md of the middleware.

Fixes #307

core/coredns.go

@@ -21,6 +21,7 @@ import (
 	_ "github.com/miekg/coredns/middleware/pprof"
 	_ "github.com/miekg/coredns/middleware/proxy"
 	_ "github.com/miekg/coredns/middleware/rewrite"
+	_ "github.com/miekg/coredns/middleware/root"
 	_ "github.com/miekg/coredns/middleware/secondary"
 	_ "github.com/miekg/coredns/middleware/whoami"
 )

core/dnsserver/config.go

@@ -17,6 +17,10 @@ type Config struct {
 	// The port to listen on.
 	Port string
 
+	// Root points to a base directory we we find user defined "things".
+	// First consumer is the file middleware to looks for zone files in this place.
+	Root string
+
 	// Middleware stack.
 	Middleware []middleware.Middleware
 

core/dnsserver/directives.go

@@ -73,6 +73,7 @@ func RegisterDevDirective(name, before string) {
 // (after) them during a request, but they must not
 // care what middleware above them are doing.
 var directives = []string{
+	"root",
 	"bind",
 	"health",
 	"pprof",